Dosimetry generally refers to the measurement of a long term absorbed radiation dose, rather than a momentary radiation quantity or rate. A dosimetry device counts the total radiation dose over some time interval. Detection of the radiation is based on the interaction between the radiation and some material. This interaction can cause physical, chemical or biological changes depending on the nature of the material and the amount of the radiation energy absorbed into the material. There are a number of different dosimetry methods currently used such as thermoluminescent dosimeters, ionization-type radiation detectors, photographic film and radiochromic materials. Each of these methods are inconvenient because they are complicated and or time-consuming and subject to error.
A dosimetry device and method are provided in U.S. Pat. No. 5,637,876 wherein the radiation dose is calculated based on optical density, that is, changes in optical properties.
Quantum dots (QDs) have been developed having desirable properties offering advantages over traditional organic dyes for biomedical applications. In particular, their optical properties depend on their size which can be tailored to be larger or smaller as required. Other advantages are: wide-band excitation, narrow-band emission (typically ⅓ of conventional fluorophores), high molar extinction coefficients, resistance to photobleaching, long fluorescence lifetimes and fluorescence intensities at least an order of magnitude better than the best organic dyes.
There is little known about the interaction of QDs with ionizing radiation. Dai et al (Unattended Radiation Sensor Systems for Remote Applications, Tromboka (ed.), CP632, pp. 220-224, [2002], American Instituted of Physics) report that semiconductor Quantum Dots (QDs) can be used as scintillators for detecting alpha particles. Letant and Wang (Nano Letters, 6, pp. 2877-2880, [2006)]) and (Applied Physics Letters, 88, 103110 [2006]) report on the use of QDs for detecting gamma radiation. Withers et al (Applied Physics Letters, 93, 173101 [2008]) report the effects of gamma irradiation on photoluminescent properties of CdSe/ZnS QDs.
There remains a need to provide improved dosimetry method and device that can easily and accurately detect ionizing radiation in a variety of applications.